Gaia and DaisyWorld

Introduction

Animated Introduction to DaisyWorld. You will need macromedia's Flash plugin to see the animation. Go do it. It is worth it.

The DaisyWorld Model

Daisyworld is a model developed in 1983 by Watson & Lovelock to describe how a simple biological interaction can affect climate in a way that is homeostatic, i.e. stabilizes temperature so that it is optimal for life. IT IS ONLY A MODEL, a thought experiment of tool that we use to help understand the concept of global homeostasis. The idea is that black and white daisies compete with each other for space to grow on a hypothetical planet. But the two plants grow at different rates as a function of temperature, black daisies outcompete white one at lower temperatures, and whites one do better at higher temperatures. Now we add the feedback effect that each daisy has on temperature - each daisy for has a different albedo (the amount of light reflected back into space), therefore, black daisies tend not to reflect light, they absorb it and, consequently heat up the planet's surface. White ones are reflective and bounce the light energy back into space and, therefore, cool the planet. To run the experiment, we seed the planet with a mix, and then slowly increase the luminosity (light reaching the planet). This is not unlike the case for Earth, since the sun's luminosity has increased gradually about 30% over 4.6 Ga.

Here's what happens:

Assignment

Question 1: What is happening to temperature over time on this graph?

Question 2: Draw a graph illustrating the temperature over time curve if the daisies did not exist on the is hypothetical planet (i.e. if the model planet were sterile).

Gaia and Albedo

Some needed terminlolgy:

  • Albedo refers to reflectivity. If an object reflects back 100% of the light (or radiation) that impinges upon it, we say it has an albedo of one (1). If an object absorbs all of the radiation it receives, the albedo is defined as zero (0). In the visible light range, an object with high albedo will look white or light coloured, a surface with low albedo will be black or dark.
  • DMSP. Dimethlysulfonioprionate (CH3C2H4CO2SCH3). Various phytoplankton release DMSP which is converted into DMS as it moves into the atmosphere from the ocean's surface.
  • DMS. DiMethylSulfide (CH3)2S. DMS is a gas that oxides into a microscopic particulate aerosol when in the atmosphere.
  • CCN. Cloud Condensation Nuclei. Clouds in the atmosphere when water vapor condenses on aerosol particles, the CCN.
  • Coccolithophorids are a class of planktonic, unucellular haptophytic algae that procuce calcareous plates (coccoliths) on their outer surface. The coccolith-producing alge are found in the fossil record from the latest Triassic through the Recent, but they peaked in the Cretaceous where they were responsible for the formation ofthe White Cliffs of Dover.

Albedo affects Earth's surface temperature. Radiation reaching Earth from the sun is either reflected back into space or absorbed by the planet. Earth as a planet acts as a “black body emitter” - it radiates the energy absorbed back into the atmosphere. (If it didn't, Earth would continually heat up and eventually melt.) But the re-radiated energy, although equal to the energy absorbed, occurs at longer wavelengths, it is shifted from the visible portion of the spectrum into the InfraRed portion. The atmospheric gasses exhibit different properties at different wavelengths, so for example, the so-called “greenhouse” gasses (CO2, CH4, H2O) pass the visible wavelengths but re-absorb the IR ones, ultimately causing the atmosphere to heat up.

It is clear from the above discussion that the amount of light reaching the surface is important in defining Earth's heat budget and to the extent that Earth's albedo is affected by biological activity, we can see a Gaian effect on climate control. One example that is commonly cited is the effect of DMS production by phytoplankton in the surface oceans. In particular, the Haptophyta (Prymnesiophytes) are capable of producing enough DMS to increase cloud production locally in the atmosphere over their blooms. Emiliania huxleyi is perhaps the most well-known of the coccolithophorids and is famous enough to have its own homepage. This species is a significant bloom-former and has been documented from outer space by satellite. Phaeocystis pouchetii is another species that produces perhaps 10% of global DMS.

Assignment: Write a paragraph describing a model in which the growth of phytoplankton is linked to climate via cloud production. Is the link between phytoplankton and climate (temperature) a positive or negative feedback system? (In a positive feedback system, if phytoplankton growth increases then temperature increases).

Web Resources

update 2 September 2003.